Reentrant Superconductivity Driven by Quantum Tricritical Fluctuations in URhGe: Evidence from $^{59}$Co NMR in URh$_{0.9}$Co$_{0.1}$Ge
Résumé
Our measurements of the $^{59}$Co NMR spin-spin relaxation in URh$_{0.9}$Co$_{0.1}$Ge reveal a divergence of electronic spin fluctuations in the vicinity of the field-induced quantum critical point at $H_R$ $\approx$ 13 T, around which reentrant superconductivity (RSC) occurs in the ferromagnetic heavy fermion compound URhGe. We map out the strength of spin fluctuations in the ($H_b$; $H_c$) plane of magnetic field components and show that critical fluctuations develop in the same limited region near the field $H_R$ as that where RSC is observed. This strongly suggests these quantum fluctuations as the pairing glue responsible for the RSC. The fluctuations observed are characteristic of a tricritical point, followed by a phase bifurcation toward quantum critical end points.